Complete bandgap for forward volume spin waves in two-dimensional magnonic lattice using YIG and Cu

Spin wave (SW) devices are emerging as the forefront of next-generation information processing due to their minimal Joule heating during information transfer. For the successful implementation of SW devices, such as logic gates [1], mastery over SW propagation is crucial. In this pursuit, we are advancing a two-dimensional (2D) magnonic crystal characterized by a periodic magnetic structure. This research presents a design using non-magnetic metal layered on a yttrium iron garnet (YIG) film, which demonstrates a complete magnonic bandgap. Within this bandgap structure, SWs are prevented from propagating in any direction, positioning it as an ideal blueprint for crafting SW waveguides to manage SW devices.

Our 2D magnonic crystal is composed of a 1 µm thick Cu film, punctuated with hexagonal apertures and slits, settled on a 10-µm-thick YIG film. The holes measure 150 µm in radius, with a lattice constant of 450 µm and slits 1 µm wide. This crystal design is anchored to dual microstrip lines (MSLs). SWs are introduced via one MSL and captured by the second. We analyzed the transmission spectra between these MSLs across a spectrum of SW incident angles on the 2D lattice, spanning 0° to 30°.

The SW transmission bands were computed utilizing the finite integral method. Within these bands, we identified two magnonic bandgaps marked by pronounced transmission decay. Notably, at a frequency of 1.795 GHz, the bandgap's spectral placement remained consistent across all incident angles, underscoring a complete bandgap. Moreover, we varied the hole radius within the structure from 25 µm to 175 µm and recalculated the transmission spectra. Structures with radii between 100 µm and 175 µm exhibited complete bandgaps, with the most pronounced bandgap (0.011 GHz) observed at a 100 µm radius. This discovery is instrumental in steering the development of SW waveguides via 2D magnonic crystals. A comprehensive portrayal of the 2D magnonic crystal structures will be presented at the symposium.

[1] T. Goto et al., Scientific Reports, 9, 16472 (2019).